The present invention relates to an X-ray film-holding device used in a cassette- or cassetteless-type X-ray photographing apparatus.
In a cassette system, an X-ray film is sandwiched between itensifying screens in a cassette, which is set in a shot position of an X-ray photographing apparatus. In a cassetteless system, on the other hand, X-ray films are taken out one by one from an unexposed film magazine, fed to a fastening device, and sandwiched between fastening plates of the fastening device in a manner such that a intensifying screen is put on each surface of each X-ray film. The fastening device travels to a shot position where an X-ray is exposed. In these prior art systems, the X-ray film is held in the cassette or fastening device with the intensifying screen sheet on each surface thereof.
For example, in a cassette-type X-ray photographing apparatus, a cassette 10 has a front plate 14 and a back plate 16 supported so as to be swingable in the directions indicated by an arrow 12, as shown in FIG. 1. One of the respective peripheral edges 18 and 20 of the front and back plates 14 and 16 is in the form of a groove, while the other is in the form of a projection. Thus, when the front and back plates 14 and 16 are joined together, the peripheral edges 18 and 20 are interlocked to prevent external light from coming into the cassette 10. The front and back plates 14 and 16 are fixed by means of metal fittings 22. A flat cushion member 24, made of sponge or felt, is fixed to the inner surface of each of the front and back plates 14 and 16. A intensifying screen 26 is pasted on each cushion member 24. An X-ray film 28 is placed between the intensifying screens 26. When the front and back plates 14 and 16 are joined together, the X-ray film 28 is sandwiched between the two plates 14 and 16 in a manner such that the intensifying screens 26 are pressed against their corresponding sides of the X-ray film 28 by the elastic force of the cushion members 24.
In this case, the cushion members 24 are flat, so that air may possibly remain between the X-ray film 28 and the intensifying screens 26 when the front and back plates 14 and 16 are joined together. In any air layer exists between the X-ray film 28 and the intensifying screens 26, the intensifying screens 26 will unevenly affect the whole surface of the X-ray film 28, and the gap between the X-ray film 28 and the intensifying screens 26, attributed to the existence of the remaining air, will produce an indistinct or blurred image. This will make diagnosis to be difficult.
Various methods are proposed to prevent air from remaining between the X-ray film and the intensifying screens. FIG. 2 is a side-sectional view showing a cassette 30 which is disclosed in Japanese Patent Publication No. 14277/70. Swingable front and back plates 32 and 34 of cassette 30 are supported by a hinge 36. A cushion plate 38 and a intensifying screen 40 are pasted on each of the front and back plates 32 and 34. An X-ray film 42 is interposed between the intensifying screens 40. The front and back plates 32 and 34 are formed on an elastic material and curved so that the distance between them is greater the further they are from the hinge 36.
Thus, as the front and back plates 32 and 34 are joined together, front end edges 44 of the contact surfaces between the X-ray film 42 and the intensifying screens 40 advance in the direction indicated by an arrow 46, as shown in FIG. 3. As a result, air is pushed forward and out from the front end edges 44 of the contact surfaces. In this cassette 30, however, an air layer 48 is liable to be produced in the central portion thereof. When the front and back plates 32 and 34 are joined together, moreover, the force of these plates 32 and 34 pressing the X-ray film 42 is even in the direction along the front end edges 44 of the contact surfaces, but is uneven in the direction of the arrow 46. In particular, in the region corresponding to the air layer 48, the front and back plates 32 and 34 are bent with maximum curvature and pressure is reduced against the X-ray film 42. If the pressure on the X-ray film 42 is uneven, the image obtained may possibly be uneven. Further, the joining of the curved front and back plates 32 and 34 requires great force.
FIGS. 4 to 6 show a cassette 50 which is disclosed in Japanese Utility Model Publication No. 33290/80. Swingable front and back plates 52 and 54 of cassette 50 are supported by hinges 56. As shown in FIG. 6, the front plate 52 is flat, and is pasted with a intensifying screen 58 on its inner surface. As shown in the vertical sectional view of FIG. 5, the central portion of the back plate 54 is protuberant. Namely, the back plate 54 has elliptic contour lines 64, indicated by dashed lines in FIG. 4, providing a maximum height y in the center. A cushion member 60 is pasted on the inner surface of the back plate 54, and a intensifying screen 58 is pasted on the cushion member 60. When the back plate 54 is swung down after placing an X-ray film 62 on another intensifying screen 58 on the front plate 52, the intensifying screen 58 on the back plate 54 comes steadily into contact with the X-ray film 62, starting from the region corresponding to the center of the back plate 54. Thus, the two intensifying screens 58 are brought closely into contact with the X-ray film 62 without leaving any air layer between them.
The back plate 54 is usually formed of an aluminum plate. It is difficult, however, to process an aluminum plate into a three-dimensional curved surface having elliptic contour lines. Since the intensifying screens 58 are rigid, they cannot easily be bent in conformity with the three-dimensional curved surfaces. Thus, it is hard to bring the X-ray film 62 uniformly into contact with the intensifying screen 58 on the back plate 54. Also in this cassette 50, the joining of the front plate 52 and the curved back plate 54 requires great force.